This invention concerns cationic core-shell particles having an acid-insoluble polymeric core and an acid-swellable polymeric shell component disposed generally about said core so that upon neutralizing said shell with acid, a portion of said shell remains attached or associated with said core. This invention further concerns polymer latex compositions wherein said polymeric shell component has been neutralized and substantially, but not totally, dissolved so as to form a blend of neutralized core-shell polymer and an aqueous solution of neutralized shell polymer. More particularly, the invention concerns the use of latex compositions produced from these cationic core-shell particles to formulate ink jet receptive coatings.
Ink jet printing is widely used to print on a variety of substrates (including paper, textiles, and plastic films). These substrates are often coated with a material that enhances their receptivity for the ink jet ink. In the case of aqueous dye-based inks, which comprise the majority of inks currently used in ink jet printing, two properties are of paramount importance. The first is an affinity for water, as the coating must absorb a large amount of water from the ink in order to obtain a print that is dry to the touch in few seconds. Ink jet ink formulations often contain over 90% water. Furthermore, the coating must maintain its physical integrity while absorbing all of this water. In other words, the receptive coating must be hydrophilic enough to absorb a large quantity of water without actually being water-soluble.
The second important property is dye fixation. The majority of aqueous ink jet inks are based on dyes rather than pigments. To obtain sharp prints with high color density, the dye molecules must be immobilized almost immediately upon contact of the ink with the substrate. Penetration of the dyes into the substrate will result in reduced color density, while lateral migration of the dye molecules will cause indistinctness in the image formed.
In order to obtain high water absorption, ink jet receptive coatings have traditionally been formulated with both hydrophilic pigments (such as silica or alumina) and hydrophilic binders. While the most commonly used hydrophilic binders are polyvinyl alcohol (PVOH) and polyvinylpyrrolidinone (PVP), other suitable natural and synthetic polymers are known in the art (e.g., gelatin, starch, polyethylene oxide (PEO), hydroxyethylcellulose, carboxymethylcellulose, and the like). Those polymers that contain hydroxyl groups (such as starch, PVOH, and PEO) are often cross-linked with a compound such as glyoxal or glutaraldehyde to render them water-insoluble while maintaining their hydrophilicity. Fully hydrolyzed polyvinyl alcohol is particularly useful because it can be dissolved in hot water and remains in solution when cooled to room temperature. When the PVOH is coated on a substrate and then dried, it will not readily redissolve in room-temperature water. However, a problem exists with use of PVOH in that PVOH has no dye trapping properties.
The dyes that are commonly employed in aqueous ink jet inks are anionic, containing sulfonic acid groups. Thus dye fixation is usually accomplished by the employment of cationic polymers, although some highly polar nonionic polymers (such as PVP and polyethyloxazoline) have a limited amount of dye fixing capability. These latter polymers fix dyes by dipolar interactions between their amide groups and the sulfonic acid groups of the dye molecules, while the cationic polymers work by the more efficient mechanism of salt formation.
The most widely used cationic dye fixative in ink jet receptive coatings is poly(diallyldimethylammonium chloride), although other water-soluble cationic polymers are known in the art. For example, U.S. Pat. No. 6,010,790 teaches the use of poly(vinylbenzylquaternary ammonium salts). Other examples of water-soluble cationic polymers are cationic starch, cationic polyvinyl alcohol, guanidine-formaldehyde resins, epichlorohydrin-polyamine condensates, and water-soluble cationic acrylic resins.
However, a problem exists with the use of both soluble dipolar polymers and soluble cationic polymers in that, unless these polymers are cross-linked in some way, their presence has a detrimental effect on the water resistance of the ink jet prints.
As an alternative to water-soluble cationic resins, cationic acrylic or styrenic latices can be used as fixatives for anionic dyes in ink jet receptive coatings. These latices behave like plastic pigments. Attaching the positive charges to the surface of a pigment particle rather than to a soluble resin greatly enhances the water resistance of the ink jet prints. However, using substantial amounts of these cationic plastic pigments in a coating also results in rheological problems, which make the coatings difficult to employ on coating machinery. Furthermore, the level of cationic charge achievable with the cationic plastic pigment may not be high enough to achieve the desired level of dye fixing.
Anionic acrylic colloidal dispersion polymeric resins are widely used in the ink and coatings industries. Such polymers are manufactured by first making an acrylic latex that contains a substantial amount of an acidic monomer (such as methacrylic acid). Usually the amount of acidic monomer is sufficient to give the polymer an acid number of about 60 to about 120. The acidic functionality of the polymer is subsequently neutralized via the employment of a base (such as sodium hydroxide, potassium hydroxide, ammonia, or a water-soluble amine). This greatly enhances the hydrophilicity of the polymer, and the latex particles first swell and then lose their discreteness. While the resulting anionic acrylic colloidal dispersion polymeric resin product appears to be clear and homogeneous on a macroscopic basis, it is actually inhomogeneous on a molecular level, having some domains that are rich in hydrophobic moieties and other domains that are rich in hydrophilic ones. If a fugitive base is employed in the neutralization, these polymer dispersions dry to form water-insoluble films.
The production of anionic polymer latexes having alkali-insoluble cores and colloidal dispersion type shells are taught in U.S. Pat. No. 4,916,171. However, these anionic polymers are unsuitable for use in ink jet coating formulations as cationicity is required for proper dye fixation.
Therefore, an object of the present invention is to avoid the major rheological problems associated with traditional binders employed in ink jet coatings by disclosing a cationic core-shell polymer latexes having an acid-insoluble polymeric core and an acid-swellable polymeric shell component.
Another object of this invention is to disclose cationic core-shell particles.
A further object of this invention is to disclose core-shell particle latexes suitable for use in formulating ink jet receptive coatings.
The objects of this invention are met via the production of cationic core-shell particles having an acid-insoluble polymeric core and an acid-swellable polymeric shell component disposed generally about said core in such a manner so that, upon neutralizing the said shell with acid, the shell polymer remains attached or associated with the particle core and becomes a colloidal dispersion. Ink jet receptive coatings formulated with latex compositions produced from these cationic core-shell particles produce prints having enhanced definition and superior color density. These coatings also exhibit excellent rheological properties, which make them suitable for use with high-speed paper coating equipment.
The cationic core-shell particles suitable for use in formulating ink jet receptive coatings comprise:
(A) a polymeric core component, said core component comprising the free radical polymerization reaction product of a mixture comprising:
(1) about 80.0% to about 99.5% by total weight of the mixture of a member selected from the group consisting of acrylic esters of alcohols containing from 1 to 22 carbon atoms, methacrylic esters of alcohols containing from 1 to 22 carbon atoms, styrene, substituted styrenes, acrylonitrile, methacrylonitrile, vinyl chloride, vinylidene chloride, vinyl ethers, vinyl esters, N-vinyl amides, acrylamides, methacrylamides, and combinations thereof; and
(2) about 0.5% to about 20.0% by total weight of the mixture of a member selected from the group consisting of ethylenically unsaturated monomers containing at least one quaternary ammonium group and combinations thereof;
(3) about 0.5% to about 8.0% by total weight of the mixture of a surfactant about selected from the group consisting of nonionic surfactants, cationic surfactants, and combinations thereof; and
(4) a catalytic amount of polymerization initiator; and
(B) an acid-swellable polymeric shell component disposed generally about said core component, said shell component comprising the free radical polymerization reaction product of a mixture comprising:
(1) about 5.0% to about 35.0% by total weight of the mixture of a member selected from the group consisting of amine-containing ethylenically unsaturated monomers and combinations thereof;
(2) about 10.0% to about 80.0% by total weight of the mixture of a member selected from the group consisting of acrylic esters of alcohols containing from 1 to 22 carbon atoms, methacrylic esters of alcohols containing from 1 to 22 carbon atoms, styrene, substituted styrenes, acrylonitrile, methacrylonitrile, vinyl chloride, vinylidene chloride, vinyl ethers, vinyl esters, N-vinyl amides, acrylamide, N-alkyl-substituted acrylamides, methacrylamide, N-alkyl-substituted methacrylamides, and combinations thereof,
(3) up to about 15.0% by total weight of the mixture of a member selected from the group consisting of ethylenically unsaturated monomers containing at least one quaternary ammonium group and combinations thereof,
(4) up to about 8.0% by total weight of the mixture of a member selected from the group consisting of ethylenically unsaturated monomers containing at least one hydroxyl group and combinations thereof,
(5) up to about 8.0% by total weight of the mixture of a member selected from the group consisting of N-hydroxymethylacrylamide, N-hydroxymethylmethacrylamide, N-alkoxymethylacrylamide, N-alkoxymethylmethacrylamide, and combinations thereof;
(6) up to about 4.0% by total weight of the mixture of a chain transfer agent;
(7) about 0.5% to about 8.0% by total weight of the mixture of a surfactant about selected from the group consisting of nonionic surfactants, cationic surfactants, and combinations thereof; and
(8) a catalytic amount of polymerization initiator.
Preferred cationic core-shell particles comprise:
(A) a polymeric core component, said core component comprising the free radical polymerization reaction product of a mixture comprising:
(1) about 85.0% to about 98.0% by total weight of the mixture of a member selected from the group consisting of acrylic esters of alcohols containing from 1 to 22 carbon atoms, methacrylic esters of alcohols containing from 1 to 22 carbon atoms, styrene, substituted styrenes, acrylonitrile, methacrylonitrile, vinyl chloride, vinylidene chloride, vinyl ethers, vinyl esters, N-vinyl amides, acrylamides, methacrylamides, and combinations thereof; and
(2) about 2.0% to about 15.0% by total weight of the mixture of a member selected from the group consisting of ethylenically unsaturated monomers containing at least one quaternary ammonium group and combinations thereof;
(3) about 1.0% to about 6.0% by total weight of the mixture of a surfactant about selected from the group consisting of nonionic surfactants, cationic surfactants, and combinations thereof; and
(4) a catalytic amount of polymerization initiator; and
(B) an acid-swellable polymeric shell component disposed generally about said core component, said shell component comprising the free radical polymerization reaction product of a mixture comprising:
(1) about 10.0% to about 30.0% by total weight of the mixture of a member selected from the group consisting of amine-containing ethylenically unsaturated monomers and combinations thereof;
(2) about 15.0% to about 80.0% by total weight of the mixture of a member selected from the group consisting of acrylic esters of alcohols containing from 1 to 22 carbon atoms, methacrylic esters of alcohols containing from 1 to 22 carbon atoms, styrene, substituted styrenes, acrylonitrile, methacrylonitrile, vinyl chloride, vinylidene chloride, vinyl ethers, vinyl esters, N-vinyl amides, acrylamide, N-alkyl-substituted acrylamides, methacrylamide, N-alkylsubstituted methacrylamides, and combinations thereof;
(3) up to about 10.0% by total weight of the mixture of a member selected from the group consisting of ethylenically unsaturated monomers containing at least one quaternary ammonium group and combinations thereof;
(4) up to about 5.0% by total weight of the mixture of a member selected from the group consisting of ethylenically unsaturated monomers containing at least one hydroxyl group and combinations thereof;
(5) up to about 5.0% by total weight of the mixture of a member selected from the group consisting of N-hydroxymethylacrylamide, N-hydroxymethylmethacrylamide, N-alkoxymethylacrylamide, N-alkoxymethylmethacrylamide, and combinations thereof;
(6) up to about 3.0% by total weight of the mixture of a chain transfer agent;
(7) about 1.0% to about 6.0% by total weight of the mixture of a surfactant about selected from the group consisting of nonionic surfactants, cationic surfactants, and combinations thereof; and
(8) a catalytic amount of polymerization initiator.
The polymeric core component comprises from about 60% to about 95% of the total weight of the core-shell particle. It is preferred that the core component constitute from about 70% to about 90% of the total weight of the particle.
The polymeric core component comprises the free radical polymerization reaction product of a mixture comprising:
(1) about 80.0% to about 99.5% (preferably from about 85.0% to about 98.0%) by total weight of the mixture of a member selected from the group consisting of acrylic esters of alcohols containing from 1 to 22 carbon atoms, methacrylic esters of alcohols containing from 1 to 22 carbon atoms, styrene, substituted styrenes, acrylonitrile, methacrylonitrile, vinyl chloride, vinylidene chloride, vinyl ethers, vinyl esters, N-vinyl amides, acrylamides, methacrylamides, and combinations thereof;
(2) about 0.5% to about 20.0% (preferably from about 2.0% to about 15.0%) by total weight of the mixture of a member selected from the group consisting of ethylenically unsaturated monomers containing at least one quaternary ammonium group and combinations thereof; and
(3) a catalytic amount of polymerization initiator.
It is preferred that the ethylenically unsaturated monomer containing at least one quaternary ammonium group employed in the production of the polymeric core component be a salt selected from the group consisting of vinylbenzyltrimethylammonium salts, acryloyloxyethyltrimethylammonium salts, acryloyloxyethyldiethylmethylammonium salts, methacryloyloxyethyltrimethylammonium salts, methacryloyloxyethylbenzyldimethylammonium salts, acryloyloxyethylbenzyldimethylammonium salts, 2-hydroxy-3-methacryloyloxypropyltrimethylammonium salts, 2-hydroxy-3-acryloyloxypropyltrimethylammonium salts, methacrylamidopropyltrimethylammonium salts, and combinations thereof; wherein said salt contains at least one counter anion selected from the group consisting of halides, sulfates, alkylsulfates, arylsulfates, and combinations thereof. It is further preferred that the counter anion be a member selected from the group consisting of chloride, bromide, methosulfate, sulfate, and combinations thereof.
The polymeric shell component comprises from about 15% to about 40% of the total weight of the core-shell particle. It is preferred that the shell component constitute from about 10% to about 30% of the total weight of the particle.
The polymeric shell component comprises the free radical polymerization reaction product of a mixture comprising:
(1) about 5.0% to about 35.0% (preferably from about 10.0% to about 30%) by total weight of the mixture of a member selected from the group consisting of amine-containing ethylenically unsaturated monomers and combinations thereof;
(2) about 10.0% to about 80.0% (preferably from about 15.0% to about 80.0%) by total weight of the mixture of a member selected from the group consisting of acrylic esters of alcohols containing from 1 to 22 carbon atoms, methacrylic esters of alcohols containing from 1 to 22 carbon atoms, styrene, substituted styrenes, acrylonitrile, methacrylonitrile, vinyl chloride, vinylidene chloride, vinyl ethers, vinyl esters, N-vinyl amides, acrylamide, N-alkyl-substituted acrylamides, methacrylamide, N-alkyl-substituted methacrylamides, and combinations thereof;
(3) up to about 15.0% (preferably up to about 10.0%) by total weight of the mixture of a member selected from the group consisting of ethylenically unsaturated monomers containing at least one quaternary ammonium group and combinations thereof,
(4) up to about 8.0% (preferably up to about 5.0%) by total weight of the mixture of a member selected from the group consisting of ethylenically unsaturated monomers containing at least one hydroxyl group and combinations thereof;
(5) up to about 8.0% (preferably up to about 5.0%) by total weight of the mixture of a member selected from the group consisting of N-hydroxymethylacrylamide, N-hydroxymethylmethacrylamide, N-alkoxymethylacrylamide, N-alkoxymethylmethacrylamide, and combinations thereof;
(6) up to about 4.0% (preferably up to about 3.0%) by total weight of the mixture of a chain transfer agent;
(7) about 0.5% to about 8.0% (preferably from about 1.0% to about 6.0%) by total weight of the mixture of a surfactant about selected from the group consisting of nonionic surfactants, cationic surfactants, and combinations thereof; and
(8) a catalytic amount of polymerization initiator.
The cationic core-shell particles of the present invention differ from traditional core-shell polymers in that the shell component contains basic groups and is acid-swellable (i.e., can be neutralized with acid). These basic groups are provided by the use of amine-functional monomers in the production of the acid-swellable polymeric shell component of the core-shell particle. Amine-containing ethylenically unsaturated monomers which are suitable for use in the present invention include those compounds containing both polymerizable ethylenic unsaturation and at least one amine group, which may be primary, secondary, or tertiary. Preferred amine-containing ethylenically unsaturated monomers include dimethylaminoethyl acrylate, dimethylaminoethyl methacrylate, diethylaminoethyl methacrylate, t-butylaminoethyl methacrylate, dimethylaminopropyl methacrylamide, allylamine, 2-vinylpyridine, 4-vinylpyridine, and the like. The amine-containing ethylenically unsaturated monomer comprises from about 5.0% to about 35.0%, preferably from about 10.0% to about 30.0%, by total weight of the mixture employed in the free radical polymerization reaction used to produce the polymeric shell component of the core-shell particle.
The dyes that are commonly employed in aqueous ink jet inks are anionic, containing sulfonic acid groups. The cationic nature of the core-shell particle serves to fix such anionic dyes. Where desired, the core-shell particle""s cationic nature may be increased by incorporating ethylenically unsaturated monomer containing at least one quaternary ammonium group in the production of the polymeric shell component at a level up to about 15.0% (preferably up to about 10.0%) by total weight of the mixture employed in the free radical polymerization reaction. Where employed, it is preferred that said ethylenically unsaturated monomer be a salt selected from the group consisting of vinylbenzyltrimethylammonium salts, acryloyloxyethyltrimethylammonium salts, acryloyloxyethyldiethylmethylammonium salts, methacryloyloxyethyltrimethylammonium salts, methacryloyloxyethylbenzyldimethylammonium salts, acryloyloxyethylbenzyldimethylammonium salts, 2-hydroxy-3-methacryloyloxypropyltrimethylammonium salts, 2-hydroxy-3-acryloyloxypropyltrimethylammonium salts, methacrylamidopropyltrimethylammonium salts, and combinations thereof; wherein said salt contains at least one counter anion selected from the group consisting of halides, sulfates, alkylsulfates, arylsulfates, and combinations thereof. It is further preferred that the counter anion be a member selected from the group consisting of chloride, bromide, methosulfate, sulfate, and combinations thereof.
Where desired, the core-shell particle may be given hydroxyl functionality via the inclusion in the free radical polymerization reaction employed to produce the polymeric shell component of up to about 8.0% (preferably up to about 5.0%) by total weight of the mixture of hydroxyl-containing monomer. Hydroxyl-containing monomers which are suitable for use in the present invention include those monomers containing polymerizable ethyleneic unsaturation and at least one hydroxyl group. Preferred hydroxyl-containing monomers include hydroxyethyl acrylate, hydroxypropyl acrylate, hydroxybutyl acrylate, hydroxyethyl methacrylate, hydroxypropyl methacrylate, butanediol monovinyl ether, allyl alcohol, and the like. The presence of hydroxyl groups in the core-shell particle facilitates the linking with cross-linking agents that are conventionally used in ink jet receptive coatings (such as aminoplast resins, glyoxal, glutaraldehyde, and the like).
Where desired, the core-shell particles may also be made self cross-linkable via the inclusion in the free radical polymerization reaction employed to produce the polymeric shell component of up to about 8.0% (preferably up to about 5.0%) by total weight of the mixture of a member selected from the group consisting of N-hydroxymethylacrylamide, N-hydroxymethylmethacrylamide, N-alkoxymethylacrylamide, N-alkoxymethylmethacrylamide, and combinations thereof.
Where desired, up to about 4.0% (preferably up to about 3.0%) by total weight of the mixture of a chain transfer agent may be employed in the shell component polymerization reaction in order to lower the molecular weight of the polymer. Preferred chain transfer agents include dodecyl mercaptan, 2-mercaptoethanol, alkyl mercaptopropionates, mercaptoacetic acid, mercaptopropionic acid, octyl mercaptan, and the like.
Surfactants suitable for use in the free radical polymerization reactions include members selected from the group consisting of nonionic surfactants, cationic surfactants, and combinations thereof Preferred nonionic surfactants include ethoxylated alkylphenols, ethoxylated fatty alcohols, ethylene oxide/propylene oxide block copolymers, and the like. Preferred cationic surfactants include, but are not limited to, the following: alkyltrimethylammonium salts wherein the alkyl group contains from 8 to 22 (preferably 12 to 18) carbon atoms and the counterion of the salt is a member selected from the group consisting of chloride, bromide, methylsulfate, and ethylsulfate; alkylbenzyldimethylammonium salts wherein the alkyl group contains from 8 to 22 (preferably 12 to 18) carbon atoms and the counterion of the salt is a member selected from the group consisting of chloride, bromide, methylsulfate, and ethylsulfate; and alkylpyridinium salts wherein the alkyl group contains from 8 to 22 (preferably 12 to 18) carbon atoms and the counterion of the salt is a member selected from the group consisting of chloride, bromide, methylsulfate, and ethylsulfate. The surfactant comprises from about 0.5% to about 8.0%, preferably from about 1.0% to about 6.0%, by total weight of the mixtures employed in the free radical polymerization reactions.
A catalytic amount of polymerization initiator is used in the free radical polymerization reactions. The amount of initiator employed commonly comprises from about 0.1% to about 3.0% (preferably from about 0.2% to about 2.0%) by weight of the total mixture used to produce the emulsion polymer. Traditional emulsion polymerization initiators (such as thermal initiators, redox initiators, and the like) are suitable for use in the emulsion polymerization reaction. Examples of suitable thermal initiators include, but are not limited to, the following: t-butyl hydroperoxide, di-t-butyl peroxide, benzoyl peroxide, benzoyl hydroperoxide, 2,4-dichlorobenzoyl peroxide, t-butyl peracetate, azobisisobutyronitrile, and isopropyl peroxycarbonate. Examples of suitable redox initiators include cumene hydroperoxide-sodium metabisulfite, cumene hydroperoxide-iron (II) sulfate, and the like. Preferred initiators include water-soluble azo compounds (such as V-50 or VA-086 manufactured by Wako Chemicals).
Where desired, the core-shell particle may comprise a plurality of shell components, each disposed about the core component.
Latexes suitable for use as ink jet receptive coatings in the present invention include aqueous suspensions of cationic core-shell particles. It is preferred that such latexes have a solids content in the range of about 25.0% to about 50.0%, with the more preferred range being about 35.0% to about 45.0%.
Preferred latexes suitable for use as ink jet receptive coatings in the present invention also include aqueous suspensions of cationic core-shell particles wherein the pH of the latex is adjusted to a level in the range of about 3.5 to about 7.0 (preferably from 4.0 to about 6.0) in order to swell or substantially, but not totally, dissolve the polymeric shell component so as to form core particles with attached colloidal dispersion polymer. Neutralization of the coreshell particles to form the pH-adjusted aqueous-dispersed latexes can be accomplished via the addition of an acid selected from the group consisting of mineral acids, water-soluble carboxylic acids, water-soluble sulfonic acids, and combinations thereof.
It is preferred to use low molecular weight carboxylic acids such as acetic acid, propionic acid, glycolic acid, lactic acid, and combinations thereof for the neutralization, as these acids will evaporate readily upon drying of the coating containing the polymer (thereby rendering the coating water-insoluble). Furthermore, these acids are less corrosive to coating equipment than are the stronger sulfonic and mineral acids.
As the acid-neutralization causes the polymeric shell component to swell and become more soluble, a substantial increase in viscosity occurs. It is preferred that these pH-adjusted aqueous-dispersed latexes have a solids content in the range of about 25.0% to about 50.0%, with the more preferred range being about 35.0% to about 45.0%.
The cationic latexes of the present invention are superior ink jet receptive coatings. Such ink jet receptive coatings can be employed to produce ink jet printable products via the process of coating a chosen substrate on at least one side with the ink jet receptive coating. Substrates which are suitable for use in producing such ink jet printable products include paper, paperboard, wood, plastic film, metal foil, textiles, and the like. Where desired, any of the pigments traditionally used in ink jet receptive coatings can be employed in the coating provided that the pigments are compatible with a cationic binder. Such pigments include, but are not limited to, the following: silica, alumina, plastic pigments, calcium carbonate, and kaolin clay.
Where desired, cationic and nonionic binders can be incorporated in the ink jet receptive coatings. These binders include, but are not limited to, the following: polyvinyl alcohol, cationic polyvinyl alcohol, polyvinylpyrrolidone, cationic vinylpyrrolidone copolymers, polyethyloxazoline, cationic water-soluble acrylic polymers, nonionic water-soluble acrylic polymers, starch, cationic starch, polyethylene glycol, methylcellulose, hydroxyethylcellulose, and mixtures thereof.
In cases where the ink jet receptive coatings contain hydroxyl functionality, cross-linkers that are traditionally used with hydroxyl-functional resins can be added to the coating. Such cross-linkers include urea-formaldehyde resins, melamine-formaldehyde resins, glyoxal, glutaraldehyde, titanates, zirconium salts, and the like.
As appreciated in the art, the exact components and properties of components desired for any coating application can vary and, therefore, routine experimentation may be required to determine the optional components and proportions of components for a given application and desired properties.
The following examples are provided to further illustrate the present invention and are not to be construed as limiting the invention in any manner.